The processing of plastic webs into bags and other like plastic members may include a relatively wide web passed through a single machine to form a plurality of bags or other members. The plastic layers in the web are sealed to each other along lines generally extended across the web by passing of the wide web through a cross sealer or a presealer having opposed seal bars spanning the web and in which the web is moved in stepped sequence. During a short seal period, the web is clamped between the seal bars to provide a thermal seal of the webs to each other. Generally, prior art cross sealers and presealers included opposed movable seal bar units which span the entire seal width of the machine. The movable seal bar structures are supported for reciprocal movement into and from engagement with each other. The movable seal bar units are secured at one end or both ends to a drive unit. A cam driven mechanism and the associated connections to the seal bars are driven by an appropriate power system such as an AC motor drive, a servo motor drive or even an air cylinder drive. The cam driven mechanism includes separate cam assemblies at each side plate of the machine with the cam assemblies secured to the opposite ends of a single rotating shaft. The respective cam assemblies are coupled to the outer ends of the seal bar and designed to move the heavy seal bar and establish an adequate seal pressure to affect the desired seal over the entire seal width of the machine. Another design has included multiple air cylinders spaced across the seal bars. The prior art machines require relatively massive seal bar structures which establish an extremely rigid bar because of the high operational seal pressures required and to produce and maintain an even pressure across the length of the seal bar. The combination of the various parts creates so much inertia that a relatively slow rate of movement is required and with a dwell control, the machine speed is significantly limited. AC motors, in particular servo motor drives, produce a better control of the sealer mechanism and particularly the movable seal bar during the start/stop sequence. The performance is not considered adequate to fully provide in-line compliant seal bar movement with a modern bag making machine. Attempts made to increase the speed of the prior art sealers resulted in significant increase in maintenance problems and associated downtimes.
A typical prior art cross sealer assembly with the wide cross seal bars often include a cloth covering applied to the seal surfaces of the seal bars to avoid attachment of the plastic webs to the sealing faces of the opposed seal bars. In such constructions, the cloth assembly is secured to the frame structure with a source roll of the cloth secured to one side of the seal bar. The cloth passes therefrom across the seal surface of the seal bar to a take-up roll which is rotatably mounted to the opposite side of the seal bar unit. Similar cloth assemblies are provided for both the upper and lower seal bar units. The cloth is typically a TEFLON material (trademark of E.I. duPont de Nemours and Company of Delaware, USA).
The wide web is often used where a plurality of laterally spaced members are formed within the single web to increase the production of product. Such machines are well known in the bag making machine for pouches and like plastic containers. A typical machine for example which had been commercially available had a web width of 1,240 millimeters. Although satisfactory bag making machines using wide cross sealers or presealers have been designed and sold, there is a need for improved cross sealers constructed to operate in a more rapid cycle time while maintaining the creation of acceptable cross seals of the plastic laminates.
The stationary seal bar unit is presently mounted within the system through a plurality of fluid cylinder units which are mounted between the frame and the seal units. It is important that the seal bar be precisely located in the operative position to affect an optimal seal of the web. The positioning may vary with the particular web material, the thicknesses of the web and the like.
In the prior art, the stationary seal bar unit is mounted with mount members and interposed fluid or as cylinder units to move the stationary seal bar unit between a seal position and alternatively in a retracted standby position.
The present invention is particularly directed to the construction of a substantially stationary seal bar unit of a wide plastic sealer machine which operates with an opposed movable seal bar structure. The movable seal bar preferably has a low inertia and is supported by a multiple of spaced mechanical linkages secured to a shaft of a common drive mechanism connected across the sealer apparatus. The rotating shaft is driven by an appropriate system, preferably a servo motor drive or a pneumatic cylinder drive, for rotating of the shaft and thereby raising and lowering of a seal bar in repetitive cycles through the spaced mechanical linkages. The multiple interconnecting mechanisms are preferably eccentric link unit or individual cam units mounted in spaced relation across the width of the sealer structure and attached to support a rigid support beam or like support structure for vertical movement. A light seal bar is secured to the support structure for movement into operative engagement with an opposed substantially rigid stationary and rigid support structure including an opposed seal bar. The seal bar is moved during the seal cycle while the substantially stationary seal bar unit does not add to the inertia of the overall seal moving system.
The present invention is directed to a construction of a substantially stationary sealed bar unit which is mounted relative to the movable seal bar unit and with the support for the stationary seal bar unit providing for limited retractive movement and relative adjustment of the operating position with respect to the movable seal bar unit. The present invention is particularly directed to the mounting support of the stationary seal bar unit within any rigid support structure. In accordance with the invention, a plurality of adjustable fluidic cylinder units secure the stationary sealed bar unit to the rigid supporting structure. Each of the fluidic cylinder units includes a fluidic cylinder which is mounted in fixed relation to the rigid support structure in alignment with a pre-determined location of the seal bar unit. The piston rod projects from the cylinder of the unit and is fixedly attached to the seal bar unit. The piston rod is secured to the cylinder piston. An adjustable piston rod is coupled to the opposite side of the piston and extends outwardly of the opposite end of the cylinder, which includes a stop wall encircling the piston rod. The outer end of the piston rod and the cylinder unit include an adjustable stop which limits movement of the piston rod. In a preferred construction, the outer end of the piston rod includes a threaded portion with a stop wall on the cylinder encircling the piston and extending outwardly from the cylinder unit. A stop nut is threaded onto the threaded portion and provides for restricted movement of the piston rod and the attached piston. This provides adjustment of the initial setting of the sealed bar unit in the effective sealing position as well as providing a proper retraction motion of the seal bar upon interruption of a sealing operation.
Thus each cylinder unit is constructed and configured for connection to the seal bar to support the seal bar in the sealing position to provide a substantially firm fixed support, but preferably allowing very limited cushioning response such that during normal operation, very slight penetration and lost motion of the seal bar is permitted. Thus the air cylinder unit functions essentially as a fixed support of the seal bar with a slight cushioning action as well as incorporating a physical repositioning of the seal bar between the operative sealing position and a retracted stand by position as well as maintaining a slight cushioning action during the operative cycle. The present invention provides an adjustable fluidic support of the relatively stationary seal bar unit, but permits the necessary repositioning and motion during a sealing operation to produce an improved thermal seal within the web.
The present invention with the multi-adjustable fluidic support across the seal bar unit produces an improved thermal seal.
The structure provides a simple, inexpensive and reliable means for interconnection into a production bag forming machine or other sealing apparatus and thereby increases the reliability and accuracy of production provided by the sealer.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.